To reduce wind flow resistance and drag on a trailer, truck, semitrailer, or other vehicle, side skirts have been used which extend downwardly from a bottom of the trailer and/or chassis toward the roadway to partially enclose the floor assembly and undercarriage.
Air flow passing under a ground vehicle imparts a drag force to the vehicle when it impinges on and flows around the vehicle undercarriage components attached to or a part of the underside of a vehicle. Side skirt systems are designed to prevent or control the flow of air from entering the undercarriage region from the side of the ground vehicle, such as a trailer of a tractor-trailer truck system, for example. Such reduction on the drag of the ground vehicle may operate to conserve fossil fuels as well as other sources of vehicle drive power for hybrid vehicles, battery-operated vehicles, and alternative fuel-based vehicles, for example.
Truck trailers typically have a higher elevation than passenger vehicles. This presents a risk that a passenger vehicle will underride the trailer in an accident, potentially resulting in damage to the underriding vehicle and injury to occupants therein. Accordingly, some trailers may include a side protection device, or underride guard, in order to reduce the risk of such passenger vehicles underriding the trailer. The side protection device is intended to reduce the extent to which a “passenger vehicle” (as defined in 49 C.F.R. Part 571§) can intrude under the side of a trailer, diminishing passenger compartment intrusion.